solve the CHAPTER MYSTERY

THE WOLF EFFECT

Eliminating wolves from Yellowstone National Park contributed to an increase in the number of elk. These elk grazed so heavily, especially along streams, that the seedlings and shoots of aspens and willows, and other trees, could not grow. Fewer trees led to fewer dams being built by beavers and to an increase in runoff and erosion. Aquatic food webs broke down, affecting birds, fish, and other animals. The recent reintroduction of wolves has caused a decrease in the overall elk population and seems to have reduced elk grazing along certain streams. That may be in part because wolves are killing more elk and in part because elk have learned to stay away from places like stream banks and valleys, where wolves can attack them most easily.

In recent years, researchers have shown that streamside vegetation is exhibiting secondary succession and that aspen and willow trees are starting to grow back. There have been numerous other changes as well. Fewer elk mean more food for smaller animals. The increase in small prey, in turn, has brought diverse predators into the community. Carcasses abandoned by the wolves provide food for scavengers. In short, organisms from every trophic level have been affected by the Yellowstone wolves.

1. Predict The Yellowstone wolf and elk are linked through a predator-prey relationship. If a disease were to strike the elk population, how would the wolves be affected?

2. Form an Opinion Yellowstone is owned by the federal government. The reintroduction of wolves there angered nearby farmers because they feared their animals would be hunted. What level of responsibility do you think national parks should have toward their neighbors?

3. Connect to the Draw a food chain that connects Yellowstone's wolves, aspen and willow trees, and elk. Then write a paragraph that explains why the Yellowstone wolves are a keystone species.